Sorry about this newbie question, especially if it has been asked before ('search' is too general to ferret out the topic).

Can a controller for a brushed or brushless motor be powered by a battery with a higher voltage rating? Does it moderate the voltage passed to the motor? If not or if the controller is likely to go up in smoke and flames, is there an electronic device - neither too heavy or large or inefficient - that can intermediate between battery and controller to match their voltage?

Similarly, does a controller with a wattage rating, say 500, limit the current to the motor such that the watts to the motor do not exceed the controller rating by much?

do you have a voltmeter too? you can use that to measure the idle current if we need to adjust the input power resistors for you.

if you use a 48V lifepo4 pack then you would wanna use a 36V controller so that the LVC of the controller does not shut it down since the 16S lifepo4 can produce current down to 32V. a 48V controller has a LVC around 40V so it will turn off before you can use all the capacity of the battery.

Open the controller and look at the caps rating.
a 12V battery is usually 14.4V off the charger once settled for SLA
so 14.4, 28.8, 43.2, 57.6
Most 48V controllers are 63V caps /4 = 15.75 hot off charger per SLA brick. I'd expect a 36V cap to at least be 50V. So a 54V (48V labelled pack) is likely to blow 50V cap.

As long as you disconnect the controller from battery when charging and measure battery to ensure below the capacitor ratings.... you might do ok, other components might not have the same stretch as the caps but usually they do.

I think dnmun meant the LVC Won't cut off
48V pack high at 58 LVC around 42-40
36V pack high at 48 LVC aroung 31-33
So a 36V controller is looking for 31V cut off on a 48V pack so your battery is damaged by too low a discharge by the time it shuts off. This is because the 36V controller is perfectly happy still operating at 33V down to 32 or 31 LVC while that 48V pack would like to shut off above 40V.

if you use a 48V lifepo4 pack then you would wanna use a 36V controller so that the LVC of the controller does not shut it down since the 16S lifepo4 can produce current down to 32V. a 48V controller has a LVC around 40V so it will turn off before you can use all the capacity of the battery.

I think he was thinking using a 48V controller with a 36V pack would shut of premature to full usage of bat pack, as a 36V pack is high at 48V and the controller would shut off at 40ish while the batts is capable of going down to 31ish.

Thanks to both of you. From what I understand here, I will NOT put a 48v battery on a 36v controller, as the initial high voltage could blow the controller circuitry.

Do you have recommendations for a line of controllers (perhaps programmable ones), monitors and throttles that would be good for enhanced setup of a brushless system? I expect the answer would be different for brushed.

By the way, the battery is an aluminum-cased, key-locked Chinese-origin unit. The controller is a fairly cheap model from tnc scooters. I could post pics but they probably would be redundant now.

I read your response together with Lessss's and concluded (wrongly? rightly?) that it has a chance of working but it would be highly dependent on the features of the particular controller, in that some 36V controllers would blow circuitry because initial (48 volt nominal) battery voltage could be as high as 58 volts. That high initial voltage could very well exceed controller operating parameters, particularly if the controller was of the cheaper variety (it is). It also sounded as though charging the lipo would best be done disconnected from the controller, which adds to daily work and wears out connections. So altogether an attempt to match the battery and controller would require additional research, operating steps and uncertainty.

it has to do with the LVC of the controller being designed for SLA batteries but people all use lithium batteries now.

like he said, the input capacitors are usually 63V in a 36V controller but the voltage of a 48V lifepo4 pack is 58V.

since we have to use the 36V controller at 58V then you should examine the input voltage regulation to determine if it needs to be hacked with a power resistor change or if it has a DC converter for the input voltage.

Open the controller, and have a look at a) the output capacitors, b) the FETs, and c) maybe the diode

The output capacitors are the big ones. The fets and diode are usually heat sunk. You need to read the partnumbers from the parts, and check the datasheet.

For a real-life example, I have a 24v controller: I wanted to run a 48V LiFePO4 pack, which is 60V fresh from charge:

Caps: They were 63v, so that's OK.

Fets: they are IRF3205's. I checked the datasheet, and found the abs. max rating of 55v. Almost good enough, but not quite. So I desoldered them, and soldered in two IRF1407PBF instead:
IRF3205: 55V, 110A, 8milliohm, TO220
IRF1407: 75V, 130A, 8milliohm, TO220. Note: it is important that ON resistance (8milliohm) is unchanged, as some?most?all? controllers measure the voltage across the ON resistance for the purpose of measuring current. So if I'd replaced the 8mohm fet with a 4mohm fet, for example, the 35A controller would then be a 70A controller with problems.
I have 100miles on the new fets with no issues.

i bet the 3205 mosfets woulda handled the full charge of the lifepo4 pack. you wanna do a precharge so the caps don't smack a voltage spike on the mosfets when you plug it in, but i bet the 3205 mosfets would work on 48V lifepo4.

you could test it by just connecting up the battery with a precharge resistor before it is fully charged and then start charging the battery while it is connected to the controller. that would be the highest voltage they would see.

If all the jargon is bogging you down, I can make it simpler. Controllers are usually inexpensive. Try your new battery setup with the old controller (odds are in your favor that it will work). If it doesn't, the worst case scenario would be you fried a controller. No harm to your batteries or motor. Replace the controller with something you like and feel will do the job. Hell, get one that could handle 60v or 72v down the road.

dnmun wrote:i bet the 3205 mosfets woulda handled the full charge of the lifepo4 pack. you wanna do a precharge so the caps don't smack a voltage spike on the mosfets when you plug it in, but i bet the 3205 mosfets would work on 48V lifepo4.
you could test it by just connecting up the battery with a precharge resistor before it is fully charged and then start charging the battery while it is connected to the controller. that would be the highest voltage they would see.

Aye, the 3205's might've worked, but it's not worth the risk, especially considering that voltages and ratings change over temperature, and the bike will be exposed to HUGE temperature ranges (middle of the night in winter, to full-power driving in the summer when the controller is stinking hot).
The new FETs were only $3 plus a half-hour of labor to swap them in, and it's *done*. If you want reliability and SAFETY, never exceed any FET's breakdown voltage (remember, the failure mode for overvoltaged fets is likely full power to the motor - your vehicle will drive away at full power, whether you are nearby or not).

if you had asked, i woulda sent you some 3205s by post. i still have a dozen i got on ebay for cheap. hard to assess the risk of failure on the road and when it would be critical. plus the time it takes to do the work.

you should measure the voltage on the 12V rail too and see if it is too high. usually the 48V conversion on a 36V controller will work but you can change the input power resistors too if needed.

lower than most want to draw down the lipo, but it should work if it cuts out under load.

Yeah, I use an external voltage/amperage logger instead. Of course I need to keep an eye on it, but that's a good idea anyway. I don't want the scooter to stop in the middle of nowhere with no power left...

My wife has a cruiser bike with four 5000mah five cell lipo batteries. I have two sets of two in parallel for a total of 42 volts if, charged to 4.2 per cell, but I don't. I messed up and broke one, now I have a three battery pack. I put them all in series for a total about 58.5 volts, because they were charged to about 3.9 per cell. I have a 350 watt, 36 volt controller, with a little 250 watt motor. I have heard that Chinese 36 volt controller's and motor setups are usually under rated because in other country's there are restrictions on speed and power. Anyway, I got on hit the throttle, waiting for smoke guess what, no problem. This bike fly's. I road for about five minutes checked the temp of the hub motor and controller. The motor was cool and the controller was only warm. I road on level ground with light throttle. DO THIS AT YOUR OWN RISK. IT SHOULD NOT WORK. I DO NOT RECOMEND IT. I DO NOT KNOW WHY. The bike is back to four cell now.

I also have a newbie question I am going to use a 72 volt battery with a 72 volt controller but what I need to know is could I use a 36 volt battery pack as a emergency backup with the 72 volt controller just to limp home or somewhere to charge my dead 72 volt dead battery incase I run out of juice or would I need to separate controllers one for the 72 volt and one for the 36 volt battery or I was even actually thinking of getting one of those luna 52 volt mini cubes for the backup instead of a 36 volt anyway that's what I need to know and just for the record I never ever thought this would ever be so intricate and technical when I started this adventure with e-bikes I thought it would just be sticking some wires together and off you go well to my surprise it is very far from that very far and thank you for any help I receive it is greatly appreciated more than words can express so thank you to everyone for your hard work and dedication